Neumann U87Ai or U87i? That is the question

What is the difference in these two models? Which is "Better"? I've seen both for around $1500 used. These mics seem to be a standard (along with their more expensive relatives) in good studios, but are they really worth the cash, or are there less expensive mics that sound "as good" or "better" than the U87?

Is a red camaro faster than a blue one? Better is a word that has a bunch of grey area in sound.All things considered and depending on how its been treated and how its aged, an 87i generally has a more 'complete' sound than one of the newer ones.However...I bought one a few years ago that really sounded like crap.Before I knew what was going on.I sold it to a savvy studio owner (not all that cheap...he didnt try to gouge me) and he sent it in for cleaning...BIG DIFFERENCE...